An unruptured congenital sinus of Valsalva aneurysm (behind the right aortic valve cusp) is described as an incidental necropsy finding in an 82 year old man. Review of previous reports on aneurysms involving only one of the three aortic sinuses discloses that few cases have been described, and that these lesions are rarely diagnosed during life. It is probable, however, that unruptured aortic sinus aneurysm (involving only one sinus) is more common than previous reports indicate, but that, among patients with congenital sinus aneurysm, rupture is likely to occur.